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Subject: Re: [f2fs-dev] [PATCH] f2fs: don't skip writeback of quota data
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-kernel@vger.kernel.org>,
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From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <4edac8af-0ae8-65e1-e3a0-a633cf81d761@huawei.com>
Date:   Thu, 16 Jul 2020 09:08:29 +0800
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On 2020/7/16 3:10, Jaegeuk Kim wrote:
> On 07/14, Chao Yu wrote:
>> On 2020/7/14 1:59, Jaegeuk Kim wrote:
>>> On 07/10, Chao Yu wrote:
>>>> On 2020/7/10 11:50, Jaegeuk Kim wrote:
>>>>> On 07/10, Chao Yu wrote:
>>>>>> On 2020/7/10 11:26, Jaegeuk Kim wrote:
>>>>>>> On 07/10, Chao Yu wrote:
>>>>>>>> On 2020/7/10 3:05, Jaegeuk Kim wrote:
>>>>>>>>> On 07/09, Chao Yu wrote:
>>>>>>>>>> On 2020/7/9 13:30, Jaegeuk Kim wrote:
>>>>>>>>>>> It doesn't need to bypass flushing quota data in background.
>>>>>>>>>>
>>>>>>>>>> The condition is used to flush quota data in batch to avoid random
>>>>>>>>>> small-sized udpate, did you hit any problem here?
>>>>>>>>>
>>>>>>>>> I suspect this causes fault injection test being stuck by waiting for inode
>>>>>>>>> writeback completion. With this patch, it has been running w/o any issue so far.
>>>>>>>>> I keep an eye on this.
>>>>>>>>
>>>>>>>> Hmmm.. so that this patch may not fix the root cause, and it may hiding the
>>>>>>>> issue deeper.
>>>>>>>>
>>>>>>>> How about just keeping this patch in our private branch to let fault injection
>>>>>>>> test not be stuck? until we find the root cause in upstream codes.
>>>>>>>
>>>>>>> Well, I don't think this hides something. When the issue happens, I saw inodes
>>>>>>> being stuck due to writeback while only quota has some dirty data. At that time,
>>>>>>> there was no dirty data page from other inodes.
>>>>>>
>>>>>> Okay,
>>>>>>
>>>>>>>
>>>>>>> More specifically, I suspect __writeback_inodes_sb_nr() gives WB_SYNC_NONE and
>>>>>>> waits for wb_wait_for_completion().
>>>>>>
>>>>>> Did you record any callstack after the issue happened?
>>>>>
>>>>> I found this.
>>>>>
>>>>> [213389.297642]  __schedule+0x2dd/0x780^M
>>>>> [213389.299224]  schedule+0x55/0xc0^M
>>>>> [213389.300745]  wb_wait_for_completion+0x56/0x90^M
>>>>> [213389.302469]  ? wait_woken+0x80/0x80^M
>>>>> [213389.303997]  __writeback_inodes_sb_nr+0xa8/0xd0^M
>>>>> [213389.305760]  writeback_inodes_sb+0x4b/0x60^M
>>>>> [213389.307439]  sync_filesystem+0x2e/0xa0^M
>>>>> [213389.308999]  generic_shutdown_super+0x27/0x110^M
>>>>> [213389.310738]  kill_block_super+0x27/0x50^M
>>>>> [213389.312327]  kill_f2fs_super+0x76/0xe0 [f2fs]^M
>>>>> [213389.314014]  deactivate_locked_super+0x3b/0x80^M
>>>>> [213389.315692]  deactivate_super+0x3e/0x50^M
>>>>> [213389.317226]  cleanup_mnt+0x109/0x160^M
>>>>> [213389.318718]  __cleanup_mnt+0x12/0x20^M
>>>>> [213389.320177]  task_work_run+0x70/0xb0^M
>>>>> [213389.321609]  exit_to_usermode_loop+0x131/0x160^M
>>>>> [213389.323306]  do_syscall_64+0x170/0x1b0^M
>>>>> [213389.324762]  entry_SYSCALL_64_after_hwframe+0x44/0xa9^M
>>>>> [213389.326477] RIP: 0033:0x7fc4b5e6a35b^M
>>>>
>>>> Does this only happen during umount? If so, will below change help?
>>>>
>>>> 	if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
>>>> +			!is_sbi_flag_set(sbi, SBI_IS_CLOSE) &&
>>>> 			wbc->sync_mode == WB_SYNC_NONE &&
>>>> 			get_dirty_pages(inode) < nr_pages_to_skip(sbi, DATA) &&
>>>> 			f2fs_available_free_memory(sbi, DIRTY_DENTS))
>>>> 		goto skip_write;
>>>
>>> Hmm, this doesn't work. The writeback was called before put_super?
>>
>> Oops, still be confused about this issue. :(
> 
> Huam, I hit the problem with the patch.
> I need to return back and think in other way. :(

Still quota data was left? what about dentry?

Thanks,

> 
>>
>> Thanks,
>>
>>> I'll try the original patch one more time.
>>>
>>>>
>>>>>
>>>>>>
>>>>>> Still I'm confused that why directory's data written could be skipped, but
>>>>>> quota's data couldn't, what's the difference?
>>>>>
>>>>> I suspect different blocking timing from cp_error between quota and dentry.
>>>>> e.g., we block dir operations right after cp_error, while quota can make
>>>>
>>>> No guarantee that there is no dirty dentry being created after
>>>> cp_error, right?
>>>>
>>>> e.g.
>>>>
>>>> Thread A				Thread B
>>>> - f2fs_create
>>>> - bypass f2fs_cp_error
>>>> 					- set cp_error
>>>> - create dirty dentry
>>>>
>>>> BTW, do you know what __writeback_inodes_sb_nr is waiting for?
>>>>
>>>>> dirty pages in more fine granularity.
>>>>>
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>>>>>>>>>> ---
>>>>>>>>>>>  fs/f2fs/data.c | 2 +-
>>>>>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>>>>>>>> index 44645f4f914b6..72e8b50e588c1 100644
>>>>>>>>>>> --- a/fs/f2fs/data.c
>>>>>>>>>>> +++ b/fs/f2fs/data.c
>>>>>>>>>>> @@ -3148,7 +3148,7 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
>>>>>>>>>>>  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
>>>>>>>>>>>  		goto skip_write;
>>>>>>>>>>>  
>>>>>>>>>>> -	if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
>>>>>>>>>>> +	if (S_ISDIR(inode->i_mode) &&
>>>>>>>>>>>  			wbc->sync_mode == WB_SYNC_NONE &&
>>>>>>>>>>>  			get_dirty_pages(inode) < nr_pages_to_skip(sbi, DATA) &&
>>>>>>>>>>>  			f2fs_available_free_memory(sbi, DIRTY_DENTS))
>>>>>>>>>>>
>>>>>>>>> .
>>>>>>>>>
>>>>>>> .
>>>>>>>
>>>>> .
>>>>>
>>> .
>>>
> .
>